ATP quantitations of functional biomass and microscopic estimates of gains in total biomass, have confirmed that Mycobacterium lepraemurium (agent of rat leprosy and for 77 years a classical obligate intracellular parasite) initiates growth in Nakamura's (1972) system. This opens the door toward the cultivation of other host dependent microbes, particularly Mycobacterium leprae. Objectives: 1. Using Mycobacterium Lepraemurium, to define conditions and factors that greatly reduce the profound physiologic "sag" of in vivo grown cells and, thus, to facilitate the fabrication of in vitro-type cell membranes. 2. To check the significance of evident progress by raising the temperature at which the cells are incubated and, as soon as progress warrants, by trials with M. leprae. 3. Oxidation-reduction potential is a fundamental physico-chemical parameter to be regulated for the sake of both in vivo grown and in vitro-adapted cells. This work is underway.